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Difficulty: HardNormal Pregnancy and Prenatal Care

A 2929-year-old woman, gravida 22, para 11, at 3636 weeks gestation presents to the clinic for a routine prenatal visit. Her pregnancy has been uncomplicated. She reports normal fetal movement and denies uterine contractions, vaginal bleeding, or leakage of fluid. Her first pregnancy was complicated by early-onset neonatal sepsis in the infant; blood cultures from the newborn grew *Streptococcus agalactiae*. The patient has a medical history significant for a severe allergic reaction to amoxicillin during childhood, which resulted in anaphylaxis and required epinephrine administration. During the current pregnancy, a midstream urine culture obtained at 1212 weeks gestation showed no growth. Her vital signs and physical examination today are unremarkable. The fetal heart rate is 145145/min. Which of the following is the most appropriate next step regarding the prevention of early-onset neonatal infection in this patient?

  1. Obtain a rectovaginal swab for *Streptococcus agalactiae* culture and antimicrobial susceptibility testingAnswer
  2. B
    Plan for empiric administration of intravenous vancomycin during labor without obtaining a screening swab
  3. C
    Plan for empiric administration of intravenous clindamycin during labor without obtaining a screening swab
  4. D
    Plan for empiric administration of intravenous cefazolin during labor without obtaining a screening swab
  5. E
    Obtain a rectovaginal swab today and plan to administer intrapartum prophylaxis only if the culture is positive

Answer

The correct action is to obtain a rectovaginal swab for culture and antimicrobial susceptibility testing.
This patient has a history of a previous infant with invasive *Streptococcus agalactiae* (Group B Streptococcus, or GBS) disease, which is an absolute indication for intrapartum antibiotic prophylaxis (IAP) regardless of current colonization status. Typically, patients with this history do not require routine rectovaginal GBS screening at 3636-3838 weeks. However, an important clinical exception exists for patients with a severe, high-risk penicillin allergy (e.g., anaphylaxis, angioedema). First-line IAP is intravenous penicillin or ampicillin, and cefazolin is used for low-risk penicillin allergies. For high-risk penicillin allergies, clindamycin is the preferred alternative. Because GBS resistance to clindamycin is highly prevalent, it can only be used if the isolate is proven susceptible via antimicrobial susceptibility testing. Therefore, this patient must have a rectovaginal swab collected now to determine clindamycin susceptibility, enabling targeted and appropriate antibiotic therapy during labor rather than defaulting to vancomycin.

Step-by-Step Solution

1
Identify the patient's baseline requirement for Group B Streptococcus (GBS) prophylaxis.
The patient has a history of a previous infant with invasive GBS disease (*Streptococcus agalactiae* sepsis), which establishes an absolute indication for intrapartum antibiotic prophylaxis (IAP) in all subsequent pregnancies.
This historical risk factor supersedes any current culture results, meaning the patient will definitely receive IAP during labor.
2
Evaluate the patient's allergy status to determine the appropriate antibiotic regimen.
The patient has a severe, high-risk penicillin allergy (anaphylaxis).
First-line IAP (penicillin or ampicillin) and low-risk alternatives (cefazolin) are strictly contraindicated due to the risk of life-threatening cross-reactivity.
3
Determine the preferred alternative antibiotic for high-risk penicillin allergies.
Clindamycin is the preferred alternative agent, but it can only be administered if the specific GBS isolate is proven to be susceptible.
There are high rates of clindamycin resistance among GBS isolates. If susceptibility is unknown, intravenous vancomycin must be used instead.
4
Formulate the immediate clinical plan for the 36-week visit.
A rectovaginal swab must be obtained today strictly for the purpose of antimicrobial susceptibility testing.
Even though the patient already qualifies for IAP and wouldn't normally need a swab, obtaining the culture allows for susceptibility testing. This promotes antibiotic stewardship by potentially allowing the use of clindamycin and avoiding empiric vancomycin.

Key Concept

Management of Group B Streptococcus (GBS) prophylaxis in pregnant patients with a previous GBS-affected infant and a severe penicillin allergy.
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Topics

Normal Pregnancy and Prenatal Care

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